Answer:
Step-by-step explanation:
Let N, J, K, M represent the numbers of cards that Martin, Josie, Kal, and Matt have, respectively.
Equations
We are told ...
 N = 12J
 J = 29 +K
 M = 14K
 K = 28
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Solution
Working from the bottom up, ...
 M = 14·28 = 392
 J = 29 +28 = 57
 N = 12J = 12·57 = 684
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The answers to the questions asked are ...
 Martin has 684 baseball cards; Matt has 392 baseball cards.